Method for constructing stabilized construction wall in unstable footing

ABSTRACT

A METHOD OF PROVIDING STABILIZATION FOR A CONSTRUCTION WALL DURING CONSTRUCTION IS AN UNSTABLE FOOTING INCLUDES THE FORMATION OF A BASIN ABOVE THE PRE-EXISTING SURFACE LEVEL OF A PROPOSED CONSTRUCTION ZONE OR SITE. THE BASIN IS USED TO RECEIVE FLUID THEREIN TO PROVIDE INCREASED HYDROSTATIC PRESSURE, ACTING ON THE WALL FROM INSIDE THE CONSTRUCTION SITE TO PROVIDE PRESSURE WITHIN THE SITE TO A DEGREE APPROXIMATING THE COUNTERVAILING PRESSURES ACTING ON THE CONSTRUCTION WALL FROM OUTSIDE THE SITE. THEN, WHILE MAINTAINING THE HYDROSTATIC PRESSURE, THE SOIL MATERIALS WITHIN THE SITE ARE REMOVED BY EXCAVATING DOWN TO A PREDETERMINED LEVEL AND REPLACED (WHILE STILL MAINTAINING THE HYDROSTATIC PRESSURE) WITH A STABILIZING FILL MATERIAL OF GREATER STRENGTH THAN THE UNSTABLE MATERIAL REMOVED FROM THE SITE. THEREAFTER, THE HYDROSTATIC PRESSURE CAN BE RELIEVED AND PREPARATION OF THE SITE CONTINUED. THE WALL STRUCTURE FORMED WILL ULTIMATELY BE CHARACTERIZED BY AN UNSTABLE FOOTING MATERIAL ON ONE SIDE OF THE WALL AT THE LOWER END THEREOF, A MAT OF STABLE FOOTING MATERIAL ON THE OTHER SIDE OF THE WALL, AND A MAT OF CONCRETE SUPERIMPOSED UPON THE MAT OF STABILIZED FOOTING MATERIAL SO THAT THE CONCRETE MAT CAN COUNTERACT LATERALLY ACTING FORCES PRESSING AGAINST THE OUTSIDE OF THE WALL.

Feb. 16, 1971 B. c. GERWICK, JR 3,563,044

METHOD FOR CONSTRUCTING STABILIZED CONSTRUCTION WALL IN UNSTABLE FOOTINGFiled March 28, 1969 2 Sheets-Sheet 1 INVENTOR. BEN C. GERWICK JR.

ATTORNEYS Feb. 16, 1971 B. c. GERWICK, JR 3,563,044

METHOD FOR CONSTRUCTING STABILIZED CONSTRUCTION WALL IN UNSTABLE FOOTINGFiled March 28, 1969 2 Sheets-Sheet z INVENTOR.

F/ 6'. /0 BEN c. GERWICK JR. BY/ 7Vr4fl fM ATTORNEYS United StatesPatent O US. Cl. 61--50 7 Claims ABSTRACT OF THE DISCLOSURE A method ofproviding stabilization for a construction wall during construction isan unstable footing includes the formation of a basin above thepre-existing surface level of a proposed construction zone or site. Thebasin is used to receive fluid therein to provide increased hydrostaticpressure, acting on the wall from inside the construction site toprovide pressure within the site to a degree approximating thecountervailing pressures acting on the construction wall from outsidethe site. Then, while maintaining the hydrostatic pressure, the soilmaterials within the site are removed by excavating down to apredetermined level and replaced (while still maintaining thehydrostatic pressure) with a stabilizing fill material of greaterstrength than the unstable material removed from the site. Thereafter,the hydrostatic pressure can be relieved and preparation of the sitecontinued. The wall structure formed 'will ultimately be characterizedby an unstable footing material on one side of the wall at the lower endthereof, a mat of stable footing material on the other side of the wall,and a mat of concrete superimposed upon the mat of stabilized footingmaterial so that the concrete mat can counteract laterally acting forcespressing against the outside of the wall.

BACKGROUND OF THE INVENTION This invention pertains to wallconstructions and methods of stabilizing same in soil conditions wherethe footing is highly unstable.

In the construction of a building, foundation walls which extend down toa predetermined depth in unstable soil conditions, e.g., where the soilis somewhat fluid or marshy or otherwise unstable, as in a swamp or thelike, may fail to encounter a proper footing or stable material. Withouta stable footing during excavation of the construction site, it will bereadily apparent that the load of earth pressure on the exteriorsurfaces of the wall can readily force the lower portion of the wallinwardly toward the construction sites as support is removed from theconstruction wall within the excavation site. However, when the bottomend of the wall is embedded in a stable soil condition, the excavationcan proceed without undue concern for the problems of the increasingpressures developing against the wall on the outside of the excavationsite.

As disclosed herein, a wall structure is provided by a method whichserves to stabilize the footing of an upright diaphragm wall structureof a type found commonly encircling a construction site.

Where the footing material is quite stable, the passive resistance ofthe material within the excavation site will ordinarily be suflicient tocounter balance the pressures acting against the exterior of the wallsurfaces.

In many instances, temporary struts have been packed against the wall toinsure a proper force counteracting the outside pressures bearingagainst the wall.

However, in highly unstable footing conditions, where the passiveresistance is quite low, the present invention 3,563,M4 Patented Feb.16, 1971 provides supporting forces acting from within the excavationsite in a controlled manner to approximate the pressures acting fromoutside the excavation site.

SUMMARY OF THE INVENTION AND OBJECTS In general, a method has beenprovided for stabilization of a construction wall in an otherwiseunstable footing material comprising the steps of forming a basin on topof the surface of a proposed construction zone or site. The basin has apredetermined depth and substantially fluid-impervious side wallboundaries including the upright wall structure which is to bestabilized. Thus, the wall to be stabilized also serves to define atleast a portion of the boundaries of the site. Then, the hydrostaticpressure acting on the wall from inside the construction site or zone isincreased to a degree approximating the countervailing pressure actingon the wall from outside the zone. This is accomplished, preferably, bythe more particular steps of filling the basin with fluid materialhaving a greater density than water so as to increase the hydrostaticpressure on the inside of the wall for countering the pressure acting onthe outside of the Wall. Then, while maintaining the increased pressure,the method contemplates removing the soil materials of the constructionsite down to a predetermined level while replacing the removed materialswith a stabilizing fill material of greater strength. Thereafter, theapplied hydrostatic pressure is removed to permit completion ofconstruction by excavating and providing a concrete mat overlaid upon apad of stable fill.

The degree of hydrostatic pressure employed within the site will, ofcourse, vary with the passive resistance of the footing material withinthe site and also with the placement and use of strut supports.

Thus, in general, pursuant to the above method of construction, there isprovided a wall structure in an unstable footing wherein an uprightdiaphragm wall is arranged in the unstable footing material in a mannerwhereby the unstable material is on one side of the wall at the lowerend of the wall while a mat of stable footing material is on the otherside of the wall. On the mat of stable material, a concrete mat issuperimposed which serves to counteract laterally acting forces pressingagainst the outside of the wall tending to force the bottom end of thewall inwardly toward the excavation.

In general, it is an object of the present invention to provide animproved wall construction technique and stabilized wall construction inan unstable footing.

The foregoing and other objects of the invention will be more clearlyapparent from the following detailed description of preferredembodiments of the invention when considered in conjunction with thedrawings.

DESCRIPTION OF THE DRAWINGS FIGS. 1-8 are schematic side elevationsection views showing a sequence of steps incorporated in the methodaccording to the invention.

FIG. 9 and FIG. 10, respectively, are plan views of two differentconstruction sites utilizing the method according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Where excavation is to takeplace on one side of a construction wall while the other side of thewall remains subject to the earth pressures acting against the wall, itis readily apparent that the footing into which the wall is embeddedmust be sufficiently firm to hold the wall at the lower end thereof andprevent the pressure on the unexcavated side from forcing the bottom ofthe wall into the excavation whereby support of the earth is lost.

By the procedure now to be described, it is possible to provide astabilized construction wall where the lower end of the Wall will beproperly supported against forces otherwise acting to move the bottom ofthe wall into the excavation. The procedure as described herein furtherproperly stabilizes the wall but in a manner whereby the bottom of thewall is not, on the other hand, forced outwardly away from theexcavation zone.

Referring to the drawings, FIGS. l8 represent a sequence of steps whichare pursued to provide stabilization to a construction wall disposedupright in an unstable footing, such as may be found, for example, in amarsh, river bed, or bay bottom or other extremely weak soil condition.

Preliminarily, depending upon site conditions, the construction zone isgraded in the region 11, as necessary, to provide a relieved outermargin disposed about the exterior of the construction lot or zone 12.Accordingly, the terrain is graded down to the existing lever 13 of lot12.

Subsequently, a diaphragm wall 14 of a type which is impervious to fluidand which is to be stabilized in its upstanding position is disposedupright in the ground 16. A suitable wall construction for this purposemay, for example, be a sheet-pile wall or, if the wall 14 is to be comea permanent portion of the building structure to be erected on the siteof the construction zone 12, it may be a slurry trench wall of the type,for example, as disclosed in US. Pat. No. 3,412,562. Each of theforegoing types of walls form an impervious fluid diaphragm satisfactoryfor the present method.

Wall 14 serves to complete the impervious boundary wall extending aboutthe construction site 12 to the extent needed. Thus, for example, whereone side of the construction site 12 is bounded by substantiallyimpervious terrain 17, the construction site 12 can be enclosed byproviding the sheet-pile walls to extend about three sides of the site12.

On the other hand, where no substantially impervious terrain isavailable, the construction site can be completely enclosed by walls 14.

The placement of Walls 14 into the earth is done in a manner to permitthe upper end of the walls to extend above the level of the surface 13of the construction site 12. Thus, the upper edge of walls 14 enclosingsite 12 form the rim of the construction zone boundaries and define abasin located above the level of the surface 13.

In order to provide a suitable location within construction site 12 fromwhich to work and conduct the construction activity, a berm 18consisting of suitable fill material is built up within site 12.

Next, a strut 19, if needed can be disposed to bear against the innerface of wall 14 and may suitably be anchored at its interior end by aconventional deadman or other anchor device 21. Thus, strut 19 serves toprovide means serving to provide lateral support to the upper end ofwall 14. It will be readily evident that other means such as the use ofconventional tie-back devices may also be employed to introduce supportto the upper end of wall 14 as desired and as feasible under thecircumstances.

Pursuant to the above preliminary steps, piles 22 may be driven into theearth for purposes of later providing support to a concrete mat 23. Thedriving of piles 22 can be accomplished by use of the driving extensionscommonly employed in driving deep piles into the ground.

Next, the basin 24 which was originally defined between the upperextension 14a of wall 14 and berm 18 and which included a bottom definedby the existing surface 13 of the construction site is filled with aheavy liquid, hereinafter referred to as a brine.

The brine must not adversely coat the stabilizing fill material, such assand, which will later replace the unstable material to be excavated outof the construction site. Thus, the brine should not cause the normallystabilizing material to become unstable by virtue of contact with theliquid brine. In addition, the brine preferably should be heavier thanwater since its purpose is to apply a supplemental hydrostatic pressureacting with passive resistance and/ or strut forces acting against thewall from within the excavation site. Thus, the inside forcesapproximate the forces acting from outside. Conditions in any givencircumstance will serve to dictate the degree of supplementalhydrostatic pressure required to properly hold the wall.

In one particular application, the brine solution has beensatisfactorily employed when consisting of a liquid having a densityrunning on the order of 75 lbs. per cubic foot as compared to theconventional weight of Water. In order to prepare suitable brinesolution, sodium chloride, calcium chloride, zinc chloride, sodiumsilicate, or mixtures of various other materials can be added to watertogether with other desirable materials such as dispersing agents,suspensions, or the like. Thus, the use of the term brine is not to belimited herein merely to the use of salt water since a number ofsuitable ways of increasing the density will be readily apparent tothose skilled in the art.

After filling the basin 24 with the brine, it will be readily apparentthat the supplemental hydrostatic pressure on the inside of the wallessentially contributes to the support force countering the supportforces acting on the outside of the wall. Then, while maintaining thesupplemental hydrostatic pressure within the construction site 12, theunstable soil material 16 are excavated from the construction site, orzone, down to a predetermined desired level 26. For example, this level26 can advantageously be located on the order of ten feet below thebottom of the structure to be built on the construction site. As notedabove, during the excavation of the unstable materials 16 from the basin24, the hydrostatic head is maintained therein by merely supplyingadditional brine material as desired by suitable means (not shown).

After reaching the predetermined level 26, a suitable stable soilmaterial is introduced, such as sand, rock, or weak mixtures ofcementitious materials, all characteristically having a relatively highinternal friction angle as compared to the internal friction angle ofthat material 16 which was removed from basin 24, is introduced. Thus.in FIG. 4, sand 27 is shown having been filled into the excavation as areplacement for the material 16 which has been previously removed.During this manipulation, the level 28 of the brine is maintainedsubstantially constant so as to ensure that the head pressure appliedagainst the inside of Wall 14 remains throughout the interchange ofstable material for the unstable material being removed.

Subsequently, substantially all of the brine is drained from the stablesoil material 27 by means of pumps 29 and hoses 31 or the like.

If necessary, as for extremely deep holes or other conditions requiringgreater strength than provided by the usual normal fill materials, suchas sand, the internal friction angle of the fill material can beenhanced by re acting materials with the brine residue so as to causecrystal growth, solidification, etc., thereby further increasing theinternal friction angle of the fill and hence improving thestabilization property of the fill material.

In addition, portions (or all) of the stabilized fill may be furtherstrengthened by intrusions of special reacting or cementing materials orspecial tremie placements of cemetitious mixtures.

After having drained the brine from the fill material 27, the strut 19can, if desired, be removed and further excavation conducted down to alevel exposing the tops of piles 22. At that point, a layer 32 of goodrock is placed around the tops of the piles 22 whereby a concrete mat 23can be formed on the tops of piles 22.

Mat 23 preferably can include a tapered or bevelled edge 33 againstwhich a strut 34 can be positioned. The other end of strut 34 can thenbe attached near the upper edge of wall 14 in a manner to providesupport between wall 14 and mat 23.

Subsequently, further excavation proceeds down through the sand 27 (orother stable material) placed into basin 24 until the only remainingstable material within the basin 24 is that which lies below the levelof the bottom of mat 23. This remaining mat portion 27a (FIG. 8) is thengraded level with the layer 32 of rock whereby additional concrete mat36 can be formed between wall 14 and mat 23. Thus, lateral support isprovided to the bottom end of wall 14 to counteract the inwardlypressing forces acting against the exterior of wall 14 at the lower end.In this manner, the lower end of wall 14 is securely stabilized.

From the foregoing, it will be apparent that the volume of the fillmaterial 27 is suflicient to stand alone in providing suflicientstability to the lower end of the wall to permit the construction of therest of the foundation to proceed as where the concrete mat 23 is thensubsequently laid taking advantage of the stable block of material 27athen located at the base of wall 14. Once mat 23 has been laid, it isthen possible to utilize struts cooperating with mat 23 and wall 14 atvarious levels to counteract inwardly pressing forces acting against thewall while the concrete of mat 36 is being poured and permitted toharden.

From the foregoing, it is also readily apparent that during one stage ofthe proceedings there is provided a construction wall structure in anunstable footing Wherein the stabilized wall construction comprisesmeans forming an upright diaphragm wall, unstable footing material beinglocated on one side of the wall at the lower end thereof while a mat ofstable footing material on the other side of the wall has been formed.Further, a mat of concrete is superimposed upon the first name mat andserves to counteract laterally acting forces pressing against theoutside of the wall.

Thus, the portion 27a forms a mat of stable footing material upon whichthe mat 36 of concrete can be applied.

In operation, the method described above serves to keep the walls 14 ofthe construction site from losing their support notwithstanding the factthat they are lodged in an unstable soil material.

What is claimed is:

1. In a method of providing stabilization for a construction wall in anunstable footing the steps comprising forming a basin upon the surfaneof a construction zone, said basin having a predetermined depth andsubstantially fluid-impervious side wall boundaries including theupright wall structure to be stabilized forming at least a portion ofsaid boundaries, applying a hydrostatic pressure to said wall frominside said zone to supplement other forces serving to resistcountervailing forces acting on said wall from outside said zone, saidsupplemental hydrostatic pressure serving to bring the forces actingfrom within said zone to a level approximating the level of forcesacting upon the wall from outside said zone, and, while maintaining saidhydrostatic pressure, removing the soil materials of said zone down to apredetermined level and replacing the removed materials with astabilizing fill material of greater strength, and thereafter removingthe applied hydrostatic pressure.

2. In the method according to claim 1 wherein the step of applying thehydrostatic pressure includes the introduction into said basin of a headof fluid pressure relative to the level of the pre-existing surface ofthe zone.

3. In the method according to claim 1 wherein the step of applying thehydrostatic pressure includes the introduction of fluid into said basinsaid fluid having a density greater than that of Water.

4. In the method according to claim 1 wherein the step of applying thehydrostatic pressure includes the introduction of a head of fluidpressure into said basin, said fluid having a density greater than thatof water.

5. In a method of providing stabilization for a construction wall in anunstable footing the steps comprising forming an upright wallsubstantially impervious to fluid to define at least a portion of theperipheral boundary of a construction zone, the top of the wallextending above the level of the pre-existing surface of said zone,completing the boundaries around said zone to extend upwardly to form abasin above the level of said preexisting surface, applying ahydrostatic pressure to act on said wall from inside said zone to raisethe forces acting on the wall from within said zone to resist thecountervailing forces acting on said wall from outside said zone, and,while maintaining said pressure, removing the soil materials of saidzone down to a predetermined level and replacing the removed materialswith a stabilizing fill of greater strength, and thereafter removing theapplied hydrostatic pressure.

6. In a method of providing stabilization for a construction wall in anunstable footing the steps comprising forming an upright wallsubstantially impervious to fluid to define at least a portion of theboundaries of a construction zone, the top of the Wall extending apredetermined distance above the level of the existing surface of saidzone, extending the rim of the zone boundaries upwards to form a basinabove the level of the existing surface of the zone, filling the basinwith fluid material to increase the hydrostatic pressure on the insideof the wall to provide a countering pressure acting to offset the forcespressing on the outside of the wall, and maintaining the appliedpressure while removing the soil materials of the zone down to apredetermined level, and replacing the removed materials with astabilizing fill of greater strength, while maintaining said hydrostaticpressure, thereafter removing the applied hydrostatic pressure.

7. In the construction of a wall structure in an unstable footing, astabilized wall construction comprising means forming an uprightdiaphragm wall, untable footing material on one side of the wall at thelower end thereof, a mat of stable footing material on the other side ofthe wall, and a mat of concrete superimposed upon the first named matserving to counteract laterally acting forces pressing against theoutside of the Wall.

References Cited UNITED STATES PATENTS 1,320,720 11/1919 Tomlinson 61-502,184,974 12/1939 Henderson 6139 2,413,867 1/1947 Easterday 61392,960,745 11/ 1960 Wallace 61-50 JACOB SHAPIRO, Primary Examiner US. Cl.X.R.

